1. Field of the Invention
The present invention relates to voltage-controlled oscillators (VCO), and more particularly, the present invention relates to a VCO that provides an improved voltage-oscillation frequency characteristic, and a related method.
2. Description of the Prior Art
In a modern information society, all kinds of knowledge, information, documents, statistics, and multimedia files are rapidly transferred, processed, managed, and stored by use of digital signals, and all kinds of corresponding digital circuits have become an important foundation for the modern information society.
As one of ordinary skill in the art would know, a phase-locked loop is widely used in many circuits, such as wired/wireless communications circuits, signal processing circuits, and even clock control sequential circuits/processors. Therefore, a stable voltage-controlled oscillator (VCO) in the PLL is a serious designed consideration.
The VCO generates an oscillating signal (or clock) with a frequency corresponding to an input voltage. In a poor VCO design, jitter affects the stability of the VCO and should be overcome.
SUMMARY OF THE INVENTION
The present invention provides a voltage controlled oscillator (VCO) with improved frequency characteristics, and a related technique. The VCO has reduced device drift and reduced jitter which protects the VCO from performance instability.
The VCO of the present invention includes a conversion circuit supplied between a bias voltage and a ground voltage for converting the control voltage into a control current, a replica bias circuit connected to the converting circuit for providing a swing voltage, and a ring oscillating circuit connected to the replica bias circuit having at least one delay unit connected in series for successively delaying an input signal as the oscillating signal after a period of delay time, wherein each delay unit has two differential input ends and two differential output ends. The replica bias circuit adjusts a supply voltage applied to the ring oscillating circuit to determine the period of delay time according to the control current and the swing voltage.
The method for providing an oscillating signal according to a control voltage in the present invention includes converting the control voltage to a control current according to a reference impedance, providing a swing voltage according to a reference current, and delaying an input signal for a period of delay time for outputting the oscillating signal. The period of delay time is determined by the control current and the swing voltage.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.